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Slide 1
Fossil vs Contemporary Carbon
at 12 Rural and Urban Sites in
the United States
Bret A. Schichtel (NPS)
William C. Malm (NPS)
Graham Bench (LLNL)
Charles E. McDade (UCD)
Judy C. Chow (DRI)
John Watson (DRI)
Urban & Rural Annual Organic Carbon
Speciated PM2.5
monitoring networks:
IMPROVE – Rural sites
STN – Urban/suburban sites
Urban & Rural Annual Organic Carbon
Carbon Isotope (14C/12C) Network
Puget Sound
Sula
Proctor Maple
Mt. Rainier
Brigantine
Rocky Mt.
Lake Sugema
Yosemite
Grand Canyon
Great Smoky Mt.
Phoenix
Tonto
Six day HI-VOL
PM2.5 samples
Summer: Jun – Aug ‘04; Winter: Dec ’04 – Feb ‘05
Summer: Jun – Aug ‘05; Winter: Dec ’05 – Feb ‘06
Summer: Jul – Aug ‘02
Contemporary (Biogenic) Vs Fossil Carbon
Mount Rainier
Contemporary or Fossil C (m g/m3)
5
fM
Contemporary
4.5
Fossil
4
C14 / C Sample

C14 / C Biogenic
AD1950
3.5
y = 0.82x
R2 = 0.95
3

2.5
2

1.5

1

0.5
y = 0.18x
R2 = 0.68
0

-0.5
0
0.5
1
1.5
2
2.5
3
3.5
Total Carbon (mg/m3)
Summer 2004
4
4.5
5
C14 half life ~5700 yr
fM = 0 for fossil C
fM ~ 1.08 for biogenic C
Fraction Contemporary
= fM /1.08
Samples corrected for
positive organic artifact
on filters
Seasonal Contemporary and Fossil C (mg/m3)
The error bars represent the range in six day concentrations
Seasonal Fraction Contemporary Carbon
The error bars represent the fraction contemporary range
Urban Excess
Puget Sound, WA (Blue) – Mt. Rainier, WA (Red)
Summer
1.5
1
0.5

2
0
Biogenic
Fossil
Total
Carbon

3
1
0

Excess:
2.4 mg/m3
98%
4
Excess:
1.66 mg/m3
56%
Biogenic
2
Excess:
1.56 mg/m3
77%
Excess:
0.23 mg/m3
11%
Fossil
2.5
Excess:
4.1 mg/m3
76%
5
3
3
Winter
6
Total
Carbon
3
Carbon (mg/m )
3.5
Puget Sound
Mt Rainier
4
Excess:
1.8 mg/m3
44%
Carbon (mg/m )
4.5
Puget Sound fossil carbon is primarily due to local sources
during winter and summer
Summer biogenic carbon is regionally distributed
~40% of the winter urban excess is biogenic carbon
 Not all biogenic carbon is “natural”
Summer



Excess:
9.6 mg/m3
89%
10
3
Excess:
0.42 mg/m3
17%
Tonto
Excess:
1.53 mg/m3
81%
Winter
12
Carbon (mg/m )
Excess:
1.94 mg/m3
45%
Excess:
5.1 mg/m3
94%
8
6
Excess:
4.5 mg/m3
84%
4
Biogenic
0
Fossil
Biogenic
Fossil
2
Total
Carbon
Phoenix
5
4.5
4
3.5
3
2.5
2
1.5
1
0.5
0
Total
Carbon
3
Carbon (m g/m )
Urban Excess
Phoenix, AZ (Blue) – Tonto, AZ (Red)
Phoenix fossil carbon is primarily due to local sources during
winter and summer
Summer biogenic carbon is regionally distributed
About half of the winter urban excess is biogenic carbon

Not all biogenic carbon is “natural”
IMPROVE Fine Particulate Carbon


All monitors were collocated with IMPROVE monitors
measuring OC and EC using thermal optical reflectance (TOR)
IMPROVE collects 24-hour PM2.5 samples every third day
Total Carbon: Summer
Total Carbon: Winter
8
8
y = 1.2x
R2 = 0.50
3
6
5
4
3
2

6
5
4
3
2
1
1
0
0
0
2
4
6
IMPROVE - TOR (µg/m3)
y = 1.12x
R2 = 0.84
7
HiVol - AMS (µg/m )
3
HiVol - AMS (µg/m )
7
8
0
2
4
6
8
IMPROVE - TOR (µg/m3)
On average HiVol total carbon was 10-20% greater than IMPROVE
Fraction Biogenic Vs EC/TC
6-Day Averages
Summer 2004
0.5
y = -0.23x + 0.43
y = -0.21x + 0.35
0.4
0.4
IMPROVE EC/TC
IMPROVE EC/TC
Winter 2004- '05
0.5
0.3
0.2
0.1
0.3
0.2
0.1
0
0
0
0.2 0.4 0.6 0.8
1
Fraction Biogenic (from C-14)
0
1.2
0.2 0.4 0.6 0.8
1
Fraction Biogenic (from C-14)
1.2
Seasonal Averages
Summer 2004
Winter 2004-05
y = -0.24x + 0.36
2
R = 0.77
y = -0.26x + 0.45
2
R = 0.86
0.4
IMPROVE EC/TC
IMPROVE EC/TC
0.3
0.2
0.1
0

0.3
0.2
0.1
0
0
0.2
0.4
0.6
Summer EC/TC
 Fossil ~ 0.36
 Biogenic ~ 0.12
 Winter EC/TC
 Fossil ~ 0.45
 Biogenic ~ 0.19

0.8
Fraction Biogenic (from C-14)
1
0
0.2
0.4
0.6
0.8
Fraction Biogenic (from C-14)
1
Winter/Summer
 Fossil: 1.25
 Biogenic: 1.58
EC/TC Ratios from IMPROVE Data Edge Analysis
IMPROVE Rural Carbon 6/04 - 2/06
IMPROVE Urban Carbon 6/04 - 2/06
3
Elemental Carbon (µg/m )
5
3
Elemental Carbon (µg/m )
5
4
3
2
1
3
2
1
0
0
0
5
10
15
20
3
Total Carbon (µg/m )
EC summer

4

Summer – 0.07
Winter – 0.16
5
10
15
20
25
Total Carbon (µg/m3)
EC winter
Rural 10th %-ile edge ~ Biogenic
EC/TC

0
25
EC summer

EC winter
Urban 90th %-ile edge ~ Fossil EC/TC
Summer – 0.41
 Winter – 0.44

Measured Primary EC/TC Ratios

Mobile Sources – Fossil Carbon





Wood Smoke – Biogenic Carbon (McDonald et al., 2000)





Softwood in fireplace: EC/TC = 0.2
Hardwood in fireplace: EC/TC = 0.1
Hardwood in woodstove: EC/TC = 0.11
Texas grass and soft and hardwood: EC/TC = 0.2 (Chow et al., 2004)
Cooking


Adjusted Roadside: EC/TC = 0.39 (Chow et al., 2004)
1996 Sepulveda. CA tunnel study: EC/TC = 0.57 (Gillies et al., 2001)
Light duty vehicle: EC/TC = 0.3 (Cadle et al., 1997)
Heavy Duty Diesel: EC/TC = 0.63 (Lowenthal et al. 1994)
EC/TC = 0.1 (Chow et al., 2004)
Secondary organic aerosol

EC/TC = 0
Comparison of EC/TC estimates
Winter
Winter
0.6
0.6
0.6
0.6
0.5
0.5
0.5
EC/TC
EC/TCRatio
Ratio
0.5
EC/TCRatio
Ratio
EC/TC
Summer
Summer
0.4
0.4
0.3
0.3
0.2
0.2
0.4
0.4
0.3
0.3
0.2
0.2
0.1
0.1
0.1
0.1
00
0
0
Fossil
Fossil
Carbon 12/14
12/14
Carbon

Literature
Literature
Biogenic
Fossil
Carbon 12/14
Carbon 12/14
Edge Analysis
Biogenic
Edge Analysis
Literature
Literature
Summer Fossil EC/TC ratio is on low side
Literature summer EC/TC higher than C 12/14 and EC/TC edge analyses


Edge
EdgeAnalysis
Analysis
Fossil
Projected fossil and biogenic EC/TC ratios are in line with other estimates


Biogenic
Biogenic
Literature examined primary aerosol
Fossil and Biogenic EC/TC is smaller in the summer than the winter indicating
some summertime SOA formation for both
Fraction Biogenic - Summer 2004-05
The summer (June-August) IMPROVE carbon data were partitioned into fossil and
biogenic carbon using the derived fossil and biogenic EC/TC ratios
Fraction Biogenic - Winter 2004-06
The summer (December - February) IMPROVE carbon data were partitioned into
fossil and biogenic carbon using the derived fossil and biogenic EC/TC ratios
Estimating Secondary Organic Carbon
(SOC)

Assume:
All elemental carbon is primary
 Winter organic carbon is primary (PC)
 Summer organic carbon is primary + secondary

EC TC W int er
 SOC 

1


 PC  Summer EC TC Summer
1
 SOC 



TC

 Summer PC SOC  1
SOC TC Summer
 SOC 

1


 OC Summer 1  EC TC Summer
Fraction Secondary OC
Fraction Secondary Organic Carbon for
Summer Months



0.5
Fossil
Biogenic
SOC / TC
SOC / OC
0.4
0.3
0.2
0.1
0
42% of the summertime organic carbon is secondary
32% of the summertime fossil carbon is secondary
If some winter organic carbon is secondary than these summer
SOC contributions are lower bounds
Summary

Biogenic carbon accounts for







80-95% of the total carbon at the rural sites
70-80% of total carbon at near urban sites
50% of total carbon at urban sites
Little seasonality and total variation in fraction
modern carbon
Urban fossil carbon is primarily due to local sources
during the winter and summer
Summer biogenic carbon is regionally distributed
40-50% of the winter urban excess is biogenic carbon

Not all biogenic carbon is “natural”
Summary


42% or more of the summertime organic
carbon is secondary
32% or more of the summertime fossil carbon
is secondary
Finished
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